[Tails-l10n] Translation platform maintenance on April 1st 2…

Hello, dear translators!

Next week the Tails translation platform will be put into maintenance
for switching the database server from MariaDB to PostgreSQL. We expect
the system to have better performance after that change (see [1] for
more info).

Maintenance is scheduled for next wednesday, April 1st 2020. So please
don't expect the platform to be working during that day.

[1] https://redmine.tails.boum.org/code/issues/16994